Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Q07: Trapped Gases Driven Out-of-EquilibriumLive
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Chair: Maren Mossman, University of San Diego |
Thursday, June 3, 2021 8:00AM - 8:12AM Live |
Q07.00001: Experimental Realization of the Many-Body Quantum Kicked Rotor Roshan Sajjad, Alec J Cao, Ethan Q Simmons, Jeremy Tanlimco, Eber Nolasco-Martinez, Hector Mas, Hasan E Kondakci, Toshihiko Shimasaki, David M Weld The kicked rotor is a paradigmatic model of classical and quantum chaos; dynamical localization in the quantum kicked rotor contrasts sharply with classically-expected ergodicity. Despite a quarter-century of atom-optical experimental studies, the effect of interactions on the dynamically localized state has remained unexplored. We report the experimental realization of a many-body kicked quantum rotor with Feshbach-tunable interparticle interactions. As interactions are increased from zero, we observe the emergence of many-body dynamical delocalization. |
Thursday, June 3, 2021 8:12AM - 8:24AM Live |
Q07.00002: Absence of heating in a uniform Fermi gas created by periodic driving Constantine Shkedrov, Meny Menashes, Gal Ness, Anastasiya Vainbaum, Yoav Sagi External trapping potentials in ultracold atoms experiments often depend on the atomic spin, which may lead to inhomogeneous broadening, phase separation and decoherence. Dynamical decoupling provides an approach to mitigate these effects by applying an external field that induces rapid spin rotations. However, a continuous periodic driving of a generic interacting many-body system is expected to heat it. We prepare a strongly interacting degenerate Fermi gas in a flat box-like potential by combining a magnetic field gradient with rf driving, which simultaneously counteracts gravitational force for two spin states with different magnetic moments. We find that there is no heating on experimentally relevant timescales for high enough driving frequency, and physical observables are similar to those of a stationary gas. In particular, we measure the pair-condensation fraction of a fermionic superfluid at unitarity and the contact parameter in the BEC-BCS crossover. The condensate fraction exhibits a non-monotonic dependence on the drive frequency and reaches a value higher than its value without driving. The contact agrees with recent theories and calculations for a uniform stationary gas. Our results establish that a strongly-interacting quantum gas can be dynamically decoupled from a spin-dependent potential for long periods of time without modifying its intrinsic many-body behavior. |
Thursday, June 3, 2021 8:24AM - 8:36AM Live |
Q07.00003: Observation of interaction-driven dynamical delocalization in a 1D quantum kicked rotor Jun Hui See Toh, Xinxin Tang, Katherine C McCormick, Subhadeep Gupta The quantum kicked rotor is known to display dynamical localization behavior, which is equivalent to Anderson localization in momentum space. Although earlier theoretical works have indicated that dynamical localization would be destroyed in the presence of interactions, it has not been experimentally observed thus far. We report on our observation of interaction-driven dynamical delocalization in a 1D quantum kicked rotor as demonstrated by a power-law growth of kinetic energy with kick number. We prepare a quantum kicked rotor system by loading a 174Yb BEC (a=5.6nm) into 1D tubes formed by a two-dimensional optical lattice derived from a 1073nm laser, and expose the system to a periodically pulsed standing-wave potential. We study the onset of delocalization in the parameter space of kick strength (controlled by pulse parameters) and interaction strength (controlled by number density), and measure the power-law exponent in the delocalized regime. Our observations of interaction-driven delocalization is strongly aided by the elimination of the transverse degrees of freedom in 1D, with the experimental setup allowing continuous tuning and observation from the 3D to the 1D regime, and to the threshold of the Tonks-Girardeau regime. |
Thursday, June 3, 2021 8:36AM - 8:48AM Live |
Q07.00004: Characterizing Quantum Turbulence in Fermionic Superfluids Michael Forbes Turbulent phenomena abound in nature, but an exact definition of turbulence remains elusive. Several features are key, including vorticity, chaotic behaviour, and energy cascades. Confirmed power-law cascades are often regarded as conclusive evidence for turbulence, but require several decades of scale, and can be difficult to extract from small experiments. In this talk I will discuss strategies for practically characterizing quantum turbulence in fermionic cold atom experiments, validated by simulating turbulent dynamics in the unitary Fermi gas on one of the largest supercomputers in the world with the recently-released W-SLDA density functional theory framework (https://wslda.fizyka.pw.edu.pl). |
Thursday, June 3, 2021 8:48AM - 9:00AM Live |
Q07.00005: Self-similar turbulence-like dynamics in a quasi-ideal Bose gasĀ Christoph Eigen, Gevorg Martirosyan, Jiri Etrych, Lena Dogra, Jake A Glidden, Timon Hilker, Robert Smith, Zoran Hadzibabic We study the dynamics of an essentially non-interacting Bose gas under strong periodic forcing. We initially prepare a quasi-pure BEC in a cylindrical optical box trap and then tune the s-wave scattering length to zero, before violently injecting energy into the system using a time-periodic spatially uniform force oriented along the box axis. We observe a rapid excitation of the initially accessible axial eigenstates, followed by a gradual leakage of energy into the (orthogonal) radial directions. The later-time momentum-resolved dynamics exhibit self-similar scaling behavior, surprisingly reminiscent of the turbulent cascade dynamics in an interacting gas, but with stark quantitative differences in the scaling exponents describing the dynamics. The non-equilibrium samples prepared in this way also provide interesting initial conditions for testing universality in the relaxation dynamics of isolated Bose gases far from equilibrium. |
Thursday, June 3, 2021 9:00AM - 9:12AM Live |
Q07.00006: Using Effective Viscosity to Characterize Quantum Turbulence in Superfluids Saptarshi R Sarkar, Praveer Tiwari, Michael Forbes Characterizing turbulence remains one of the most interesting unsolved problems in physics. By forming tangles of quantized vortices, cold-atom experiments can now be used to study turbulent phenomena. Imaging limitations, however, pose a challenge for experiments: how can one identify turbulent states with available experimental probes? We hypothesize that hydrodynamic shockwaves will provide a way to characterize the nature of the underlying quantum turbulence. In this work we use dynamical simulations to quantify how microscopic quantum turbulence manifests through the emergence of an effective viscosity. We extract the effective viscosity by fitting quantum simulations with classical hydrodynamic models, providing a connection between classical and quantum turbulence. Validating this procedure with cold atoms allows us to construct similar theories for understanding the turbulent structures on large scales, such as might arise in neutron stars. |
Thursday, June 3, 2021 9:12AM - 9:24AM Live |
Q07.00007: Kolmogorov number in a turbulent Bose gas Lena Hannah Dogra, Timon Hilker, Jake A Glidden, Gevorg Martirosyan, Christoph Eigen, Jiri Etrych, Robert Smith, Zoran Hadzibabic Turbulence phenomena are present in a vast variety of physical systems, from water waves to the early universe. We use a homogeneous Bose gas of 39K to study turbulent cascades, in which energy injected at the low-momentum scale is transported in momentum space with constant energy flux towards higher momenta. This leads to a scale-invariant momentum distribution defined by the so-called Kolmogorov exponent and Kolmogorov number, the amplitude. Here we investigate the dependence of the Kolmogorov number on the transported energy flux, and observe universal relations in agreement with the theoretical predictions for wave turbulence. |
Thursday, June 3, 2021 9:24AM - 9:36AM Live |
Q07.00008: Observation of Real-Time Dynamics of a Direct Turbulent Cascade in a Bose FlatlandĀ Maciej Galka, Andrey Karailiev, Martin Gazo, Panagiotis Christodoulou, Nishant Dogra, Julian Schmitt, Zoran Hadzibabic Turbulence is a universal nonequilibrium phenomenon encountered in various systems including the early universe, nonlinear optics, classical and quantum fluids. Despite its ubiquity, turbulence is still not fully understood as it requires solving a chaotic many-body problem over different length scales. Here, we follow an alternative approach to study turbulence and its origin by using an ultracold atomic system which is conceptually simpler and provides easy experimental tunability of relevant microscopic parameters like dimensionality, interaction strength, etc. In particular, we study the dynamics of a two-dimensional Bose gas held in a box trap and driven far from equilibrium. |
Thursday, June 3, 2021 9:36AM - 9:48AM Live |
Q07.00009: Homogeneous and Isotropic Quantum Turbulence Across the BEC-BCS Crossover Khalid Hossain, Saptarshi Sarkar, Andrea Barresi, Gabriel Wlazlowski, Piotr Magierski, Michael Forbes Quantum turbulence is the dynamics of a tangle of interacting quantized vortices in a superfluid system. These interactions enable energy transfer across different length scales in the system leading to power-law Kolmogorov scaling: a characteristic of turbulence. We hypothesize that evidence for these scaling laws will be seen in the largest simulations of fermionic superfluids to date, but will need correction due to finite size effects. By adjusting the interaction strength over the BEC-BCS crossover, we can tune the size of the vortex cores, exploring how this impacts the observed scaling behavior. In this talk, we will present results from one of the largest fully microscopic simulations of fermionic superfluids, and show how effects like the vortex core size impact the scaling. These simulations connect the microscopic dynamics of vortices to the macroscopic models for quantum turbulence in neutron stars, laying the groundwork for understanding phenomena such as pulsar glitches. |
Thursday, June 3, 2021 9:48AM - 10:00AM Live |
Q07.00010: Non-equilibrium dynamics of driven Fermi Condensates using three species Johannes Kombe, Corinna Kollath, Kuiyi Gao, Michael Koehl We study the non-equilibrium response of a strongly interacting, harmonically trapped Fermi gas following an effective quench of the interaction strength. The quench is realised by a complete population transfer of one of its constituting species to a third internal level via a radio-frequency pulse. The Fermi gas is modelled as a three-component Hubbard model, and we use the time-dependent matrix-product state method to gain insights into the condensate dynamics of the fully interacting fermionic gas in the low density limit. We observe non-trivial pairing dynamics influenced by the excitation of a collective mode of the trap and its interplay with the arising density inhomogeneity. These findings are compared to recent experimental results. |
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